Saw Animator

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Description

The
Saw
Animator module is a very interesting module when you whish to get
that FAT sound, usually obtained with two or more sawtooth VCOs, but
you are short of VCOs. You can get this typical sound with
only one sawtooth VCO, thanks to Bernie Hutchins (JAES, 1981). The
Digisound 80 has this wonderful module and Scott Bernardi designed a
version of its own. The present module is a somehow simplified but yet
efficient version. To get the best of this module, it must be used in
conjunction with a mixer. I chose not to integrate a mixer within the
module in order to benefit
from the dry outputs which are very useful when used with a LFO instead
of a VCO. When used with a sawtooth LFO and inputing fixed CVs in the
MOD
inputs, one can achieve some interesting phase shifted modulators such
as quadrature modulation. Well the possibilities are numerous and it's
up to your imagination...

A basic saw animator patch would be :

Here are a sound samples of the saw-animator using the above patch.
These sound clips are 12s long and start with 3s of the raw sawtooth
then the ouputs of the module are mixed in.

8'
sawtooth, output #1 with slow rate

8'
sawtooth, output #1 with fast rate

8'
sawtooth, output #1 and output 2 both with slow rate

8'
sawtooth, output #1 and output 2 both with fast rate

8'
sawtooth, output #1 with slow rate and output #2 with fast rate

16'
sawtooth, output #1 and output #2 both with slow rate

16'
sawtooth, output #1 and output #2 both with fast rate

Schematic

IMPORTANT NOTE : the circuit has been
designed to work with balanced sawtooth signals ranging from -5V to 5V,
if you intend to use it with unbalanced sawtooth or different peak to
peak voltage you will have to recalculate some resistor values...
Two 100pF capacitors are not shown on this schematic diagram because
they are optional. These are to be used to remove spikes at the output.
If such spikes are visible, connect these capacitors in parallel to R15
and R30. The PCB was designed with pads for these optional capacitors.

Printed Circuit Board and Component Layout

NOTE : the PCB and a
component kit for this module are now made available by Bridechamber

PCB design

Layout

Download
the
schematic as a PDF file
Download the PCB as a PDF file

WARNING !
The
document is formatted to be printed directly on a mylar for
photo-etching or a "press & peel" paper. Make sure that when the
printed face of mylar is in contact with the copper side of the PCB,
the lettering can be read normally.

List of parts and building instructions

reference

value

number

U1,U2,U3

TL074

3

Q1,Q2

BC547C

2

D1,D2,D3,D4

1N4148

4

R1,R2

10 ohm

2

R17,R32

1k

2

R6,R21

1.5k or 2.2k

2

R5,R20

4.7k

2

R7,R22

15k

2

R3,R14,R15,R16,R18,R29,R30,R31

47k

8

R8,R9,R10,R11,R12,R13,R23,R24,R25,R26,R27,R28

100K 1%

12

R4,R19

120K

2

C7,C9

100pF* optional

2

C3,C5,C5

100nF

3

C6,C8

2.2µF Wima 63V
(or 2x1µF polyester film)

2

C1,C2

22µF/25V electro.

2

T2,T4

100K 10 turns trimmer

2

T1,T3

250K or 220K 10 turns
trimmer

2

LD1,LD2

yellow LED

2

P1,P2

1M rev log potentiometer

2

Jk1,Jk2,Jk3,Jk4,Jk5,Jk6

6,5 mm jack socket

6

Note that in most cases C7 and C9
may be omitted !
For R6 and R21, the value can be selected between 1.5K and 2.2K
depending on the brightness and current draw of the LED, try 2.2K and
if you find the LED are not bright enaough diminish this value.

Wiring

The
wiring diagram is only valid for the latest version of the PCB (june
17th 2007)!

Front plate

Panel
design

Download
the
silkscreen mask as a PDF file

Download the silkscreen mask as a JPEG file

Trimming

There are four trimmers to be
adjusted. Note that the adjustment procedure is the same for T1 and T3
and for T2 and T4.

Setting of T1 (SHAPE trimmer).

ground the MOD IN #1 input

feed a balanced sawtooth (ranging -5V to 5V) to the SAW IN
#1 input

connect an oscilloscope to the OUTPUT #1 output

check the shape of the output signal, it should look
like one or another of the following waveshapes

adjust T1 in order to obtain a normal sawtooth
waveshape

Setting of T2 (BALANCE trimmer)

adjust T2 in order that the output signal is balanced and
ranges from -5V to +5V

Unground the MOD IN #1, you must see the sawtooth swaying at the rhythm
of the internal LFO